Cbp1p is required for message stability following 5′-processing of COB mRNA

Cbplp is a nuclear encoded protein required for the stabilization of mitochondrial COB mRNA, which codes for apocytochrome b in the yeast Saccharomyce8 cerevisiae. The COB gene is cotranscribed with the upstream tRNA^Glu gene. Release of tRNA^Glu from the initial transcript generates a precursor mRNA with a 5′-end at position -1098. The 5′-end of mature COB message is generated by cleavage of the pre-mRNA at nucleotide -955 or -954. Previous work indicated that Cbp1p acts through cis-elements near these cleavage sites. Here we have tested whether Cbp1p stabilizes COB mRNA solely by stimulating the processing of COB precursor RNA at nucleotide -955/-954. Yeast strain TG955 was constructed such that the -955 COB mRNA 5′-processing site coincides with the upstream tRNA 3′-endonuclease site at position -1098, allowing the 5′-end of COB mRNA to be formed by the tRNA 3′-processing enzyme. Respiratory growth and stability of COB mRNA in TG955 are Cbp1p-dependent. Therefore, we conclude that Cbp1p is important for the stabilization of COB mRNA after 5′-processing.